In the treatment of garbage or refuse it is a standard practice to sort the refuse into a plurality of fractions, usually into a heavy fraction including all of the pieces of relatively great surface density, by which is meant articles having a relatively high ratio of weight to surface area, and a light fraction including all of the pieces of relatively light surface density. Air classifiers, flotation systems, electromagnetic strippers, and the like can be used to separate the heavy fraction into various recyclable subfractions.
It has, however, proven a relatively complex task to separate the light fraction into several subfractions. In particular it is highly desirable to separate the synthetic-resin foil and textile pieces on one side from the paper pieces on another. The paper industry requires for making new paper from recovered old paper that the old paper used have a minimum content of foil and textile material.
Hitherto the sole method of separating the light fraction into two subfractions as described above has required the use of a large vessel filled with water. The entire light fraction is charged into this water-filled vessel and is separated therein into the desired two subfractions. This system has the considerable disadvantage that is requires an expensive and large installation. Furthermore it is necessary, after the separation, to centrifuge the two subfractions so as to recover the water used in the process. Overall such a procedure is generally so expensive as normally to make it economically unattractive so to separate the light fraction.